While network access users have increasing demands for time-critical multimedia content, most popular content is created for consumption in a stationary environment, such as broadcast TV news programs. Because of mobility and resource constraints, network access users are normally unable to watch an entire program in order to know what is happening. Furthermore, different users have interests in different contents. Broadcasting multimedia content, therefore, may not be desirable for network access users, especially for mobile users. Instead, relevant multimedia content needs to be extracted according to a user's interest and delivered in a timely manner. The industrial prototype system underlying this invention provides such a service using multimedia messages.
Delivering multimedia messages to a network access device uses wireless and user interfaces which are known to be two of the most power-hungry components in a networked handheld device. The inventors' measurement and analysis show that 30 multimedia messages could easily exhaust the energy supply of a commercial Smartphone.
It is worth noting that while most other low-power system design efforts have focused on the device itself, e.g. better power management or dynamic voltage scaling policies, the invention examines the entire ecosystem in which a network access device operates; encompassing servers, middleware, embedded systems, network access devices, and user interfaces. Such an extension reveals great energy-saving opportunities.
The following is a description of a network access device used for a study of the power issue and a description of an existing multimedia messaging system.
Although cellular phones can enjoy the 2.5 G/3 G data services and WiFi networks provide a higher data rate, at the time of this writing, GPRS is the most widely available data access method. The invention employs an Audiovox SMT5600 Smartphone with GPRS from Cingular, as a typical network access device. System information is presented for the Audiovox SMT5600 in the following table.
WirelessGPRS Class 10 and BluetoothOSWindows Mobile 2003 SEDisplay2.2 inch, 176 × 220 TFT LCD with64K ColorsBattery1064 mA-HourAudioIntegrated loud-speaker
Power status was obtained by measuring the voltage drop cross a 100 mΩ sense resistor embedded in the power supply cord with a USB-1608FS module. A summary chart of the data collected on power usage follows.
ComponentExtra power (mW)Idle 20System busy370LCD 13LCD LightingBetween 56-212GPRSUp to about 1600BluetoothPENDINGBetween 1-3TRANSFERUp to about 300LoudspeakerAbout 45
Note that “Idle” power is the basic case when the system is idle with the display turned off. The other cases have power consumption required by the corresponding components compared to the idle case. For example, the entry of “System busy” is the power consumption when the system is repeatedly carrying out discrete-cosine transforms (DCTs) as compared with the idle case. Note that loudspeaker power consumption can vary significantly, depending on the duty cycle incurred by the sound. The LCD lighting power data is for typical luminance for night-time reading. The GPRS power also can vary significantly, depending on the cellular network quality. “Bluetooth TRANSFER” is the power used by Bluetooth transmission at 115 Kbps data rate.
The table also shows the power demands of the user interface (display and loudspeaker) and for the wireless communication. Such a profile is typical for most Smartphones and handheld devices.
The existing multimedia messaging system FIG. 1 (Prior Art) is an industrial prototype service that delivers customized multimedia content to mobile users. It automatically monitors a large number of TV content feeds 102, extracts the content 110 that matches user interest profiles 104, repurposes the content 114, and delivers repurposed content to network access devices 118 according to device profiles 108. The system consists of a media processing platform (102, 110, 116) and a content delivery platform (104, 106, 112, 114, 118).
The prototype's FIG. 1 media processing platform (102, 110, 116) continuously records selected broadcast TV programs from several broadcasters using satellite or cable feeds based on a predetermined schedule and according to the interests 104 of the target audience. These structured video feeds from broadcast television are digitized, compressed and stored in a database 116. The user profile record 104 is processed to identify the content that is relevant to each user. A content repurposing module 114 processes the content and generates a presentation that fits the target device. The user profile includes an interest profile 104 and a device profile 108 for the user. An Interest Profile 104 consists of a number of topics, each of which is defined by a set of keywords, and is provided by the user via a Web interface. The delivery method as well as the content presentation depends on the user's Device Profile 108, which specifies the device characteristics such as display resolution and connectivity type. The device profile 108 is also provided by the user via a Web interface. The content delivery platform has gateways that manage the interfaces to network access devices with a plurality of protocols and servers. The network access devices 118 may be as simple as numeric pagers to as complex as handheld devices capable of playing video.
A typical situation for the Audiovox Smartphone is the prototype system finding a news story matching a user's interest profile. The prototype system extracts a pertinent video segment, repurposes the content to fit the target device, and delivers the message to the user through the standard GPRS-based multimedia messaging service (MMS). Upon receiving the message, the phone notifies its user. The user then takes out the phone and downloads the entire MMS message. Such a process, unfortunately, is not only interruptive but also consumes significant power on the network access phone device.
The energy cost in the Audiovox Smartphone from a 70 second video message of CNN's coverage on eBay's acquisition of Skype is shown in the following table. This table also shows the energy cost by the text and key frame versions of this same message.
Message FormatTextKeyframesVideoSize (Byte)16010K696KDownloadingAutomatic~0.03~1.2~80energy (Joule)Manual~0.08~1.7~114Consuming energy (Joule)~5~10~48
Note that the exact energy cost may vary, depending on external factors such as cellular network quality and user behavior. The data presented were averaged over several measurements. Note that “Downloading energy,” energy consumption by downloading the message, is different for automatically fetching and manual downloading. Manual downloading incurs additional display energy, as the display typically remains on while a user waits for the download to finish. “Consuming energy” is the energy consumption for the user to access the message, which is mostly consumed through display. It is assumed that text is consumed with a typical reading rate of 300 words per minute, four key frame images are consumed with 4 seconds/shot, and video is consumed during play time with the speaker on. Note that the prototype system provides entire messages in a predefined MMS format for cellular phones.
This table offers many insights. First, the energy cost of a video clip message is extremely high. The Audiovox Smartphone will run out of battery if the user receives and consumes 90 such messages, even without any other usage. Second, the energy costs of different media formats differ drastically by orders of magnitude. It is therefore possible to trade information richness for a longer battery lifetime. Third, manual downloading costs more than 40% more energy, mostly because of the power needs of the display. Fourth, “Consuming energy”, especially by the display, dominates whether the message is delivered as text or key frames.
Therefore there remains a need for cost-effective techniques to improve the original prototype system for better battery lifetime and usability.